Note: Descriptions are shown in the official language in which they were submitted.
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Use of Carboxamides for the Treatment of Tinnitus
The present invention relates to new pharmaceutical uses of carbamazepine
derivatives.
More particularly the present invention relates to new pharmaceutical uses of
the
carbamazepine derivatives of formula I
R~
R2
N
H2 O
wherein
(a) Ri represents hydrogen, and R2 represents hydroxy or Ci-C3alkyl
carbonyloxy, or
(b) R, and RZ together represent an oxo group,
and of their pharmaceutically acceptable salts.
The preparation of the compound of formula I wherein R, is hydrogen and R2
represents
hydroxy and of its pharmaceutically acceptable salts is described, e.g., in US
3,637,661.
Such compound, monohydroxycarbamazepine, (10-hydroxy-10,11-dihydro-
carbamazepine),
the main metabolite of the antiepileptic oxcarbazepine (Trileptal ~) is well
known from the
literature [see for example Schuetz H. et al,, Xenobiotica (GB), 16(8), 769-
778 (1986)j. The
compound is indicated to be suitable for the treatment of psychosomatic
disturbances,
epilepsy, trigeminal neuralgia and cerebra( spasticity.
The preparation of the compound of formula I wherein R1 is hydrogen and R2
represents Ci-
C3alkyl carbonyloxy and of the pharmaceutically acceptable salts thereof is
described, e.g.,
in US 5,753,646. The compounds are described to be efficacious against
epilepsy.
The carbamazepine derivatives of formula I wherein R1 represents hydrogen, and
R2
represents hydroxy or C,-C3alkyl carbonyloxy constitute chiral compounds. For
the purposes
of the present invention, the chiral compounds disclosed herein can be
employed in the form
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of racemates, in mixtures comprising one enantiomer in excess (e.g., more S-10-
hydroxy-
10,11-dihydro-carbamazepine than R-10-hydroxy-10,11-dihydro-carbamazepine) or
in
enantiomerically pure form (e.g. pure S-10-hydroxy-10,11-dihydro-carbamazepine
or pure S-
10-acetoxy-10,11-dihydro-carbamazepine).
The compound of formula ( wherein R1 and R2 together represent an oxo group is
known as
oxcarbazepine (10-oxo-10,11-dihydro-5H-dibenz[b,f]azepine-5-carboxamide,
marketed e.g.
under the brand name Trileptal~). Oxcarbazepine is a known anticonvulsant drug
useful in
the treatment of seizures of, for example, epileptic origin. Its preparation
is described, e.g., in
the German patent 2,011,087.
Tinnitus is the medical term for roaring, buzzing, clicking, whistling,
hissing, or high pitched
ringing in the ears or inside the head. Tinnitus may be constant or occur
intermittently in one
or both ears. Although there are many theories about how tinnitus occurs,
there is no
scientific consensus to its origin. Some causes of tinnitus result from a blow
to the head,
large doses of aspirin, anemia, noise exposure, stress, impacted wax,
hypertension and
certain types of medications and tumors.
The term "other inner ear/cochlear excitability related diseases" as used
herein includes, but
is not restricted to neuronal loss, hearing loss, sudden deafness, vertigo or
Meniere's
disease.
In accordance with the present invention, it has now surprisingly been found
that the
compounds of formula I in free base or acid addition salt form is useful in
the prevention and
treatment of tinnitus and other inner ear/cochlear excitability related
diseases.
Hence, the present invention relates to the use of a compound of formula I
wherein
(a) R1 represents hydrogen, and R2 represents hydroxy or C1-C3alkyl
carbonyloxy, or
(b) R1 and R2 together represent an oxo group,
or pharmaceutically acceptable salts thereof for the treatment of tinnitus or
other inner
ear/cochlear excitability related diseases.
In one preferred embodiment of the present invention, R1 represents hydrogen
and R2
represent hydroxy.
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In another preferred embodiment of the present invention, R, represents
hydrogen and R2
represents acetoxy.
In a further preferred embodiment of the present invention, Ri and R2 together
represent an
oxo group.
The activity in tinnitus of the compounds can be shown in standard tests, e.g.
in the
salicylate-induced tinnitus model in rats, or in tinnitus models in cats, and
in particular in
those models described herein.
It has been demonstrated [C.A. Bauer et al., Hearing Research 147 (2000) 175-
182] that
chronic salicylate exposure causes upregulation of glutamic acid decarboxylase
(GAD)
expression in the rat inferior colliculus (IC), associated with the
development of tinnitus.
Furthermore, electrophysiological recordings from auditory neurons using patch
clamp
recording techniques [D. Peruzzi et al. Neuroscience 101 (2000) 403-416, X.
Lin et al.,
Journal of Neurophysiology 79 (1998) 2503-2512] and single neuron recordings
[J.J.
Eggermont and M. Kenmochi, Hearing Research 117 (1998) 149-160] showed that
the
excitability of neurons is changed following salicylate and quinine treatment.
Administration of salicylate or quinine caused an increase in the firing rate
auditory neurons
measured by extracellular electrophysiological recording techniques. Using in
vitro
electrophysiological recording techniques superfusion with salicylate
increases the
excitability of the recorded neurons. On administration of the compounds at
concentrations
of about 1 nM to 300 wM, the effects of salicylate were reversed.
The pharmacological activity of the compounds of formula I may, for example,
also be
evidenced in clinical studies known as such. Such clinical studies are
preferably randomized,
double-blind, clinical studies in patients with tinnitus. The beneficial
effects on tinnitus can be
determined, e.g., directly through the results of these studies.
For the treatment of tinnitus and the other conditions mentioned herein,
appropriate dosage
will of course vary depending upon, for example, the specific compound of
formula I
employed, the host, the mode of administration and the nature and severity of
the condition
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being treated. However, in general, satisfactory results in animals are
indicated to be
obtained at a daily dosage of from about 1 to about 300 mg/kg animal body
weight. In larger
mammals, for example humans, an indicated daily dosage is in the range from
about 10 to
about 3000 mg of a compound of formula I, conveniently administered, for
example, in
divided doses up to four times a day.
The compounds of formula I may be administered in any usual manner, e.g.
orally, for
example in the form of tablets or capsules, or parenterally, for example in
the form of
injection solutions or suspensions.
The present invention also provides pharmaceutical compositions comprising a
compound of
formula I in association with at last one pharmaceutical carrier or diluent
for use in the
treatment of tinnitus. Such compositions may be manufactured in conventional
manner.
Unit dosage forms may contain for example from about 2.5 mg to about 1000 mg
of a
compound of formula I.
The invention further provides the use of a compound of formula I for the
manufacture of a
pharmaceutical composition for the treatment of tinnitus and other inner
earlcochlear
excitability related diseases such as neuronal loss, hearing loss, sudden
deafness, vertigo or
Meniere's disease.
The invention further provides a method for the treatment of tinnitus and
other inner
ear/cochlear excitability related diseases such as neuronal loss, hearing
loss, sudden
deafness, vertigo or Meniere's disease in a subject in need of such treatment,
which
comprises administering to said subject a therapeutically effective amount of
a compound of
formula I.
Racemates of compounds of formula I wherein Ri represents hydrogen and R2
represents
hydroxy or C~-C~alkyl carbonyloxy can, e.g., be obtained by mixing the pure
enantiomers of
the respective compound of formula I. The pure enantiomers of a compound of
formula I
wherein R~ represents hydrogen and R2 represents hydroxy or C1-C3alkyl
carbonyloxy can
be obtained starting from the racemate by procedures known as such. The
racemate may be
separated into its enantiomers through the formation of diastereomeric salts,
for example by
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salt formation with an enantiomer-pure chiral acid, or by means of
chromatography, for
example by HPLC, using chromatographic substrates with chiral ligands.
In one embodiment of the invention, the pure enantiomers of the compound of
formula I
wherein R1 represents hydrogen and R2 represents hydroxy are prepared
according to the
procedures described in the Examples.
The pure enantiomers of the compound of formula I wherein R1 represents
hydrogen and R2
represents Ci-C3alkyl carbonyloxy can be prepared, e.g., according to the
procedures
described in US 5,753,646 or W002/09257.
The term "enantiomerically pure form" as used herein means that a chiral
compound is
almost free of its enantiomer, i.e., a sample of the chiral compound comprises
less than
about 5, preferably less than about 2, more preferably less than about 0.5,
weight percent of
its enantiomer.
Hence, the present invention relates to the use of a compound of formula I,
wherein Ri
represents hydrogen and R2 represents hydroxy or C1-C3alkyl carbonyloxy,
especially
acetoxy, wherein the compound is employed in enantiomerically pure form, in
particular of a
compound of formula I having the S configuration.
The following Examples serve to illustrate the invention without limiting the
invention in its
scope.
Abbreviations
Ac acetyl
aqu. aqueous
dansyl 5-(dimethylamino)-1-naphthalenesulfonyl
Et ethyl
HPLC high pressure liquid chromatography
Me methyl
NMR nuclear magnetic resonance
RT room temperature
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THF tetrahydrofuran
Ts tosyl
Examples
Example 1: Procedure for the enantioselective Transfer Hydrogenation of 10-Oxo-
10,11-
dihydro-dibenzo[b,tjazepine-5-carboxylic acid amide to R(-)-10,11-Dihydro-10-
hydroxy-5H
dibenz[b, f]azepine-5-carboxamide
To a mixture of 10-oxo-10,11-dihydro-dibenzo[b,tjazepine-5-carboxylic acid
amide (300 mg,
1.189 mmol) and RuCI[(1 R,2R)-p-TsNCH(C6H5)CH(CsHS)NH2](ns-p-cymene, Aldrich,
Switzerland) (8.8 mg, 0.0138 mmol) in CH2CI2 (15 ml) is added dropwise a
premixed solution
of formic acid and NEt3 (5:2, 328 mg:289 mg) at 23 °C and stirred for
10 min. The clear
solution is heated to reflux for 16 h. The reaction mixture is cooled to RT,
diluted with CH2CI2
(20 ml) and neutralised with aqu. NaHC03. After washing with brine the
solution is
concentrated under reduced pressure. The residue is purified by flash
chromatography on
silica gel using a 6:1 EtOAc-MeOH mixture as eluent to afford of R(-)-10,11-
dihydro-10-
hydroxy-5H dibenzo[b,t]azepine-5-carboxamide (enantiomeric purity (ee) > 99 %
determined
by HPLC on Chiracel OD, Retention time: 9.46 min. [a]p'' _ -195.3 °
(ethanol).'H-NMR (400
MHz, CDCI3):7.70-7.20 (m, 8 H), 5.30 (br s,1 H), 5.10-4.60 (br s, 2 H), 3.75-
3.40 (m, 1 H),
3.20-2.90 (m, 1 H), 2.50 (br s, 2 H). NMR-Datas refer to Lit.: Benes, J et
al., J. Med Chem.
1999, 42, 2582-2587. Molecular weight: 254.291
Example 2: Procedure for the enantioselective Transfer Hydrogenation of 10-Oxo-
10,11-
dihydro-dibenzo[b,t]azepine-5-carboxylic acid amide to S(+)-10,11-Dihydro-10-
hydroxy-5H
dibenz[b, fJazepine-5-carboxamide
To a mixture of 10-oxo-10,11-dihydro-dibenzo[b,f]azepine-5-carboxylic acid
amide (300 mg,
1.189 mmol) and RuCI[(1 S,2S)-p-TsNCH(CsHS)CH(C6H5)NH2](ns-p-cymene) (11 mg,
0.0173
mmol) in CHzCl2 (15 ml) is added in two portions a premixed solution of formic
acid and NEt3
(5:2, 656 mg:578 mg) at 23 °C and stirred for 10 min. After that formic
acid is added (50 NI)
and the clear solution is heated to reflux for 16 h. The reaction mixture is
cooled to RT,
diluted with CH2CI2 (20 ml) and neutralised with aqu. NaHC03. After washing
with brine the
solution is concentrated under reduced pressure. The residue is purified by
flash
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chromatography on silica gel using a 6:1 EtOAc-MeOH mixture as eluent to
afford of S(+)-
10,11-dihydro-10-hydroxy-5H dibenzo[b,t]azepine-5-carboxamide (ee > 99 % by
HPLC on
Chiracel OD). Retention time: 12.00 min. [a]p'' _ +196.6 ° (ethanol).'H-
NMR (400 MHz,
CDCI3):7.70-7.20 (m, 8 H), 5.30 (br s,1 H), 5.10-4.60 (br s, 2 H), 3.75-3.40
(m, 1 H), 3.20-
2.90 (m, 1 H), 2.50 (br s, 2 H). NMR-Datas refer to Lit.: Benes, J et al., J.
Med. Chem.
1999, 42, 2582-2587. Molecular weight: 254.291
Alternative production: To a mixture of 10-oxo-10,11-dihydro-
dibenzo[b,t]azepine-5-
carboxylic acid amide (300 mg, 1.189 mmol) and RuCI[(1 S,2S)-p-dansyl-
NCH(C6H5)CH(C6H5)NH2](ns-p-cymene) (8.5 mg, 0.012 mmol) in CH2CI2 (15 ml) is
added
dropwise a premixed solution of formic acid and NEt3 (5:2, 328 mg:289 mg) at
23 °C and
stirred for 10 min. The clear solution is heated to reflux for 16 h. The
reaction mixture is
cooled to RT, diluted with CH2CI2 (20 ml) and neutralised with aqu. NaHC03.
After washing
with brine the solution is concentrated under reduced pressure. The residue is
purified by
flash chromatography on silica gel using a 6:1 EtOAc-MeOH mixture as eluent to
afford of
S(+)-10,11-dihydro-10-hydroxy-5H dibenzo[b,tJazepine-5-carboxamide.
Example 3: Preparation of RuCI[(1 S,2S)-p-dansyINCH(C6H5)CH(C6H5)NH2](r)6-p-
cymene)
a) Preparation of (S,S)-5-dimethylamino-naphthalene-1-sulfonic acid (2-amino-
1,2-diphenyl-
ethyi)-amide: To a solution of (S,S)-diphenylethylenediamine (250 mg, 1.2
mmol) and
triethylamine (0.5 ml) in THF is added dropwise a solution of dansyl chloride
(318 mg, 1.2
mmol) in THF (2 ml) at 0°C. After stirring 16 h at RT the solvent is
removed in vacuum and
the residue is resolved in methylenchloride (20 ml). The organic solution is
washed with
NaHC03 solution (5 ml), dried over Na2S04 and after filtration the solvent is
removed. Flash
chromatographie afford (S,S)-5-dimethylamino-naphthalene-1-sulfonic acid (2-
amino-1,2-
diphenyl-ethyl)-amide as yellow oil which crystallizes by drying in vacuum. M:
445.59.'H-
NMR (400 MHz, CDCI3):8.36 (t, J= 7.5 Hz, 2 H), 8.17 (dd, J= 7.2, 1.2 Hz, 1 H),
7.47 (dd, J=
8.8 Hz, 1 H), 7.34 (dd, J= 8.5 Hz, 1 H), 7.24-7.16 (m, 4 H), 7.11 (d, J= 7.5
Hz, 1 H), 6.99-
6.74 (m, 6 H), 4.61 (d, J= 8.5 Hz, 1 H), 4.20 (d, J= 8.5 Hz, 1 H), 2.80 (s, 6
H).
b) Preparation of f3uCl~('1 S,2S)-p-dansyINCH(C6H5)CH(C6H5)NHzJ(ris p-cymene):
A solution
of (S,S)-5-dimethylamino-naphthalene-1-sulfonic acid (2-amino-1,2-diphenyl-
ethyl)-amide
(80mg, 0.18 mmol), NEt3 (36 mg, 0.36 mmol) and [RuCl2(p-cymene)]2 (55 mg,
0.09mmol) in
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_g_
2-propanol is heated at 80°C for 1 h. The solvent is removed after that
and the dark red
residue is washed with water (2 ml). The solid is dried in vacuum and used
without any
purification. M: 715.34.
